The present embodiment relates generally to methods for cementing in a wellbore, designing a well, constructing a well, and wells constructed according to such methods.
In the drilling and completion of an oil or gas well, a wellbore is drilled, and one or more pipe strings or casings are introduced into the wellbore. A cement composition is introduced into the wellbore and forms a cement sheath that cements the casing(s) into place.
It is understood that one of the objectives of the cement sheath is to achieve and maintain zonal isolation. Throughout the life of a well, however, the well encounters stresses that can compromise the integrity of the cement sheath, and therefore compromise zonal isolation. Stress can be caused by pressure or temperature changes in the wellbore, which are often the result of activities undertaken in the well bore, such as pressure testing, well completion operations, hydraulic fracturing, steam injection and hydrocarbon production.
For example, in a cyclic steam well, the cement sheath in the wellbore is stressed by the temperature rise and injection pressure during a steam injection cycle in the well. Such temperature and pressure rise causes expansion of the casing held in place by the cement sheath, which expansion puts tensile stress and compressive stress loadings on the cement sheath and can result in compromised zonal isolation or complete failure of the cement sheath. In addition, wellbores in formations that are not able to provide much confining stress to hold the cement sheath in place during these injection cycles are much more susceptible to failure of the cement sheath.
Thus, stresses that occur within a wellbore can cause radial cracks in the cement sheath, crushing of the cement composition or shear failure, de-bonding between the cement composition and the wellbore, or de-bonding between the cement composition and one or more casing(s). Each of the foregoing cement failures compromises zonal isolation.